Clonidine is a central antihypertensive drug that stimulates α2 receptors. Patches using clonidine are commercially available in the form of a formulation including deposited crystals. Such clonidine patches can maintain their effect for a long period of time, about one week, after application to the skin. However, the clonidine patches have a problem in that transdermal absorbability changes due to temperature changes during storage. At present, there are no effective measures for the above problem. Therefore, in clinical sites, clonidine patches are required to be stored under strict temperature control such that the temperature does not exceed, for example, 30° C. Accordingly, the storage of clonidine patches imposes a heavy burden on clinical sites.
Patent Literature 1 discloses a clonidine patch comprising a medicated layer containing polyisobutylene (PIB), mineral oil (MO: liquid paraffin), colloidal silica, and clonidine, wherein the ratio of MO to PIB is 1.0 or higher, and the viscosity of the medicated layer is 1.5×107 or higher. The use of such a medicated layer allows the desired transdermal permeability (transdermal absorbability) and viscosity (cohesion) to be ensured. However, there is no description that the transdermal absorbability of the clonidine patch changes due to temperature changes during storage.
Patent Literature 2 discloses a clonidine patch comprising an adhesive layer which is formed on a backing and contains: a copolymer including, as essential components, an alkyl (meth)acrylate having an alkyl group with an average carbon number of 4 or more and a vinyl ester having a polarity parameter of 0 or less; dissolved clonidine; and a dispersed organic acid salt of clonidine. The use of such an adhesive layer prevents the reaction of clonidine with the adhesive and also prevents crystals of clonidine from depositing. However, the technique disclosed in Patent Literature 2 cannot be used for a clonidine patch formulated using only clonidine free base.